Switching converter to operate in pulse width modulation mode or pulse skipping mode

ABSTRACT

An electronic device includes a current comparator to generate an output current based upon a difference between a current flowing in an output branch and a current flowing in an input branch. A pair of transistors is coupled to an output of the current comparator. A first amplifier has inputs coupled to the pair of transistors and to a reference voltage, the first amplifier being configured to subtract the reference voltage from a voltage across the pair of transistors and output a difference voltage. A second amplifier has inputs coupled to the difference voltage and to the reference voltage, the second amplifier being configured to subtract the difference voltage from the reference voltage and output a pulse skipping mode reference signal.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/218,605, filed Jul. 25, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/531,314, filed Nov. 3, 2014, and now U.S. Pat.No. 9,423,816, which claims priority from Chinese Application for PatentNo. 201410537583.1 filed Oct. 11, 2014, the disclosures of which areincorporated by reference.

FIELD OF THE DISCLOSURE

This disclosure relates to the field of DC to DC switching powerconverters, and, more particularly, to switching power converters thatreduce power consumption of electronic devices.

BACKGROUND

As technology has evolved, handheld battery powered electronic devices,such as cellular phones and tablets, have grown in functionality,processing power, and screen resolution. As consumers now spend greaterperiods of time using these devices than in the past, a market desirefor such devices to have a long battery life has emerged. At the sametime, however, to ease the portability and enhance the aesthetics ofsuch devices, a market desire for such devices to be as small aspossible for a given screen size has emerged. These market desires canbe at odds with each other, as a simple way to increase battery life isto increase the size of the battery in the device, however, such anincrease in battery size may result in an increase in the size of thedevice itself.

One way to increase the battery life of a device that may not result inan increase in size of the device may be to reduce the power consumptionof the device. To that end, such devices may switch between an activemode in which the device is actively performing functions, and a standbymode in which the device is passively performing functions, or even notperforming functions. Since such devices may spend more time in thestandby mode than the active mode, a reduction of power consumption inthe standby mode may result in a significant increase in battery life.

These electronic devices may employ a power supply to power theircircuitry. The power supply may convert the output of the battery intoconsistent and usable power, and in some cases, a switching powerconverter may be employed as the power supply. Such a switching powerconverter may employ a pulse-width modulation (PWM) technique to controlthe power delivered to the circuitry in the active mode. While PWM maybe efficient for controlling the power delivered to the circuitry in theactive mode, a different modulation technique may be desirable forcontrolling the power delivered to the circuitry in the passive mode.For example, a pulse frequency modulation (PFM) mode or a pulse skippingmodulation (PSM) mode may be desirable for control of the powerdelivered to the circuitry in the passive mode, as these modes may beable to sufficiently operate the circuitry in the passive mode whiledelivering less power than would be delivered by a PWM technique,thereby decreasing power consumption.

Fine control of the transition threshold of the switching converterbetween PWM and PFM/PSM modes can help to further reduce powerconsumption, and thus increase battery life of the device. To that end,developments in circuitry to finely control this transition thresholdare desired.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

An electronic device may include a switching converter configured toconvert an input voltage to an output voltage, and being selectivelyoperable in a pulse skipping mode based upon a control signal. Theswitching converter may include a comparator having a first inputconfigured to receive an error signal, a second input configured toreceive a skipping mode reference signal, and an output configured togenerate the control signal. In addition, a reference generator may beconfigured to generate the skipping mode reference signal as a functionof a difference between the output voltage and the input voltage.

The switching converter may include an error amplifier having a firstinput configured to receive a feedback signal derived from the outputvoltage, a second input configured to receive an error reference signal,and an output configured to generate the error signal.

The reference generator may include a first current generator configuredto generate a first current as a function of the input voltage, and asecond current generator configured to generate a second current as afunction of the output voltage. The reference generator may also includea differencing circuit configured to generate a difference current as afunction of a difference between the first and second currents, and aconversion circuit configured to convert the difference current to theskipping mode reference signal.

The conversion circuit may include a pair of transistors configured tooutput a conversion voltage, and a first amplifier having a first inputconfigured to receive the conversion voltage, a second input configuredto receive an error reference signal, and an output configured togenerate a difference voltage as a function of a difference between theconversion voltage and the error reference signal.

The pair of transistors may include a first transistor having a firstconduction terminal configured to be coupled to the difference current,and a second conduction terminal, and a second transistor having a firstconduction terminal configured to be coupled to the second conductionterminal of the first transistor, and a second conduction terminalconfigured to be coupled as feedback to the output of the firstamplifier. The second conduction terminal of the first transistor andthe first conduction terminal of the second transistor may cooperate togenerate the conversion voltage as a function of a voltage drop acrossthe second diode coupled transistor.

The conversion circuit may also include a second amplifier having afirst input configured to receive the error reference signal, a secondinput configured to receive the difference voltage, and an outputconfigured to generate the skipping mode reference signal as a functionof a difference between the difference voltage and the error referencesignal.

The electronic device may also include a voltage divider configured tocouple the error reference signal to the first input of the secondamplifier, and an input resistor configured to couple the differencevoltage to the second output of the second amplifier. A feedbackresistor may be coupled between the input resistor and the output of thesecond amplifier. A resistance of the input resistor may match aresistance of the feedback resistor.

The first current generator may include a first current generatorresistor and a first current mirror having an input and an output. Afirst current generator input transistor may have a control terminalconfigured to be coupled to the input voltage, a first conductionterminal configured to be coupled to the first current generatorresistor, and a second conduction terminal configured to be coupled tothe input of the first current mirror. The output of the first currentmirror may be configured to generate a first mirrored current as afunction of a current flowing through the first current generator inputtransistor.

The first current generator may include a second current mirror havingan input configured to be coupled to the output of the first currentmirror, and an output configured to generate the first current as afunction of the first mirrored current.

The second current generator may include a second current generatorresistor, and a third current mirror having an input and an output. Asecond current generator input transistor may have a control terminalconfigured to be coupled to the output voltage, a first conductionterminal configured to be coupled to the second current generatorresistor, and a second conduction terminal configured to be coupled tothe input of the third current mirror. The output of the third currentmirror may be configured to generate the second current as a function ofa current flowing through the second current generator input transistor.

The differencing circuit may include a current comparator having a firstinput configured to receive the first current, a second input configuredto receive the second current, and an output configured to generate thedifference current as a function of a difference between the firstcurrent and the second current.

The electronic device may include one of a mobile telephone, a tablet,and an integrated circuit package.

Another aspect is directed to another electronic device. This electronicdevice may include a switching converter. The switching converter mayinclude an error amplifier having a first input configured to receive afeedback signal derived from a second voltage, a second input configuredto receive an error reference signal, and an output configured togenerate an error signal. A first comparator may have a first inputconfigured to receive the error signal, a second input configured toreceive a skipping mode reference signal, and an output configured togenerate a pulse skipping mode control signal. A second comparator mayhave a first input configured to receive the error signal, a secondinput configured to receive a width modulation mode reference signal,and an output configured to generate a pulse width modulation controlsignal. Control logic may be configured to be coupled to the pulseskipping mode control signal and the pulse width modulation controlsignal. In addition, an output transistor may be configured to becoupled to the control logic and a first voltage, and configured tooutput the second voltage based upon the control logic. A referencegenerator may be configured to generate the skipping mode referencesignal as a function of a square root of a difference between the secondvoltage and the first voltage.

A method aspect is directed to a method of operating a power converter.The method may include generating a skipping mode reference signal as afunction of a difference between an output voltage and an input voltage,using a reference generator. A control signal indicating that pulseskipping mode is to be entered may be generated based upon an errorsignal and the skipping mode reference signal, using a comparator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electronic device in accordance withthis disclosure.

FIG. 2 is a schematic diagram of the reference generator of theelectronic device of FIG. 1.

DETAILED DESCRIPTION

One or more embodiments of the present disclosure will be describedbelow. These described embodiments are only examples of the presentlydisclosed techniques. Additionally, in an effort to provide a concisedescription, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions may be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentdisclosure, the articles “a,” “an,” and “the” are intended to mean thatthere are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

Referring initially to FIG. 1, an electronic device 100 is nowdescribed. The electronic device 100 may be a cellular phone, a tablet,or any other portable battery powered device. In addition, theelectronic device 100 may also be an integrated circuit. The electronicdevice 100 includes a switching converter 110 that is configured toconvert an input voltage Vin to an output voltage Vout in either a pulsewidth modulation mode or a pulse skipping mode. The pulse widthmodulation mode is used for active operation of the electronic device100 (for example, in the case where the electronic device is a cellularphone, the active mode might include making a voice call, browsing theinternet, or playing a multimedia file), while the pulsed skipping modeis used for passive operation of the electronic device (here, in thecase where the electronic device is a cellular phone, the passive modemight include an idle state with the display off).

The switching converter 110 includes an error amplifier 112 thatreceives a feedback signal Vfb derived from the output voltage and anerror reference signal Vref as inputs, and generates an error signalVerr at its output. A first comparator 116 receives the error signalVerr and a skipping mode reference signal Vskip_mode at its inputs, andgenerates a pulse skipping mode control signal PSM at its output. Theskipping mode reference Vskip_mode signal is generated by the referencegenerator 200 as a function of the difference between the output voltageVout and the input voltage Vin. As will be explained in detail below,the function may be the square root of the difference between the outputvoltage Vout and the input voltage Vin.

A second comparator 118 receives the error signal Verr and a pulse widthmodulation mode signal Vpwm (which may be a sawtooth waveform) at itsinputs, and generates a pulse width modulation control signal PWM at itsoutput. Control logic 120 is coupled to the outputs of the firstcomparator 116 and second comparator 118, as well as a clock signal froman oscillator 122. The control logic 120 is coupled to the gateterminals of the PMOS transistor 126, and the NMOS transistor 124, andoperates these transistors so as to deliver power to the load 132 ineither a pulse skipping mode or a pulse width modulation mode. Dependingon the output of the control logic 120, current will flow from Vin,through the inductor 128, and either the PMOS transistor 126 (during aportion of the cycle during which power is to be delivered) or the NMOStransistor 124 (during a portion of the cycle during which power is notto be delivered). When the NMOS transistor 124 is on (thus, during aportion of the cycle during which power is not to be delivered), currentthat flows through the inductor 128 is stored. If the output of thecontrol logic 120 is such that the current flows through the PMOStransistor 126, the current flows then through the load 132, which iscoupled in parallel with a capacitor 130. In addition, if current wasstored in the inductor 128, it flows therefrom to the load when the PMOStransistor 126 is on (thus, during a portion of the cycle during whichpower is to be delivered). If the output of the control logic 120 issuch that the current flows through the NMOS transistor 124, the currentthen flows to ground.

The current flowing through the inductor 128, in pulse skipping mode,can be represented mathematically as:

$\begin{matrix}{{Ipeak} = {\frac{Vin}{L}*d*T}} & (1)\end{matrix}$

where d is the duty cycle of the device, and T is the switching period.As will be understood by those of skill in the art, current transfers tothe load 132 during the d₂T period. d₂ can be represented mathematicallyas:

$\begin{matrix}{d_{2} = {\frac{Vin}{{Vout} - {Vin}}*d}} & (2)\end{matrix}$

the load current can thus be represented mathematically as:

$\begin{matrix}{{I_{o}*T} = {\frac{I_{peak}}{2}*d_{2}*T}} & (3)\end{matrix}$

Therefore, the equation can be simplified as:

$\begin{matrix}{I_{o} = {{\frac{I_{peak}}{2}*d_{2}} = {{\frac{I_{peak}}{2}*\frac{Vin}{{Vout} - {Vin}}*d} = {\frac{Vin}{2*L}*d*t*\frac{Vin}{{Vout} - {Vin}}*d}}}} & (4)\end{matrix}$

Thus, the load current, as simplified, can be represented mathematicallyas:

$\begin{matrix}{{Io} = {\frac{{Vin}^{2}}{2*{L\left( {{Vout} - {Vin}} \right)}}*d^{2}T}} & (5)\end{matrix}$

By modeling the load as an equivalent sense resistor, the voltageproportional to the current across the inductor 128 can bemathematically represented as:

$\begin{matrix}{{Vc} = {{{Ipeak}*{Rsens}} = {\frac{Vin}{L}*d*T*{Rsens}}}} & (6)\end{matrix}$

Solving ford yields:

$\begin{matrix}{d = {\frac{Vc}{{Vin}*{Rsens}*T}*L}} & (7)\end{matrix}$

Plugging this value of d into the equation for Io yields:

$\begin{matrix}{{Io} = {\frac{{Vc}^{2}}{2*\left( {{Vout} - {Vin}} \right)*{Rsens}^{2}*T}*L}} & (8)\end{matrix}$

This can be rewritten as:

$\begin{matrix}{{Io} = {\frac{{Vc}^{2}}{\left( {{Vout} - {Vin}} \right)}*K}} & (9)\end{matrix}$

where K is:

$\begin{matrix}{K = \frac{L}{2*{Rsens}^{2}*T}} & (10)\end{matrix}$

The reference generator 200 will now be described in greater detail withreference to FIG. 2. The reference generator 200 includes a firstcurrent generator 210 that generates a first current I1 as a function ofthe input voltage Vin, and a second current generator 220 that generatesa second current I2 as a function of the output voltage Vout. Adifferencing circuit 230 generates a difference current Id as a functionof the difference between the first and second currents. A conversioncircuit 240 converts the difference current Id to the skipping modereference signal Vskip_mode.

The first current generator 210 will now be described in more detail.The first current generator 210 includes a first current generator inputtransistor 250 that has its control terminal coupled to the inputvoltage Vint, and has its conduction terminals coupled to a firstcurrent generator resistor R1 g and the input of a first current mirror212. The first current mirror 212 mirrors the current I1 flowing throughthe first current generator input transistor 250 to its output, which iscoupled to the input of a second current mirror 214. The second currentmirror mirrors the current I1 to its output as the first current appliedto the differencing circuit 230.

The second current generator 220 will now be described in more detail.The second current generator 220 includes a second current generatorinput transistor 252 that has its control terminal coupled to the outputvoltage Vout, and has its conduction terminals coupled to a secondcurrent generator resistor R2 g (which has the same resistance as thefirst current generator resistor R1 g in the illustrated embodiment) andto the input of a third current mirror 254. The third current mirror 254mirrors the current I2 flowing through the second current generatorinput transistor 252 to its output as the second current to thedifferencing circuit 230.

The differencing circuit 230 is a current comparator that receives thefirst current I1 and second current I2 as inputs, and generates adifference current Id at its output. The difference current Id is equalto a difference between the first current I1 and the second current I2,and can be described mathematically as:

${Id} = \frac{{Vout} - {Vin}}{R\; 1g}$

It should be noted that although R1 g is used in the equation above, R2g could have been used instead, as the resistors have the sameresistance in the illustrated embodiment.

The conversion circuit 240 will now be described in greater detail. Theconversion circuit 240 includes a pair of transistors 242 a, 242 bconfigured to output a conversion voltage Vconv, and in an arrangementthat will be described in more detail below. The conversion voltageVconv is received by an input of a first amplifier 244, while a secondinput of the first amplifier receives the error reference signal Vref.The first amplifier 244 generates a difference voltage Vd at its outputas a function of the difference between the conversion voltage Vconv andthe error reference signal Vref.

The first transistor 242 a has a first conduction terminal coupled tothe difference current Id, a second conduction terminal coupled to afirst conduction terminal of the second transistor 242 b, and a controlterminal also coupled to the difference current Id. The secondtransistor 242 b also has a second conduction terminal coupled asfeedback to the output of the first amplifier 244, and a controlterminal coupled to the different current Id. The coupling between theconduction terminals of the first transistor 242 a and the secondtransistor 242 b serves to generate the conversion voltage Vconv as afunction of a voltage drop across the second transistor.

The pair of transistors 242 a, 242 b and the first amplifier 244together form a square root circuit. The difference voltage Vd, asoutput by the first amplifier 244 can therefore be describedmathematically as:

${Vd} = {{Vref} - {K\; 1*\sqrt{{Vout} - {Vin}}}}$${{where}\mspace{14mu} K\; 1} = \frac{.59}{\sqrt{\mu \; n*{{Cox}\left( \frac{W}{L} \right)}*R\; 1g}}$

A voltage divider comprised of the resistors Rdiv1 and Rdiv2 (which haveequal resistance values in the illustrated embodiment) couples the errorreference signal Vref to the input of a second amplifier 248. An inputresistor Rin couples the difference voltage to the input of the secondamplifier 248, and a feedback resistor Rfb (which has the sameresistance as the input resistor in the illustrated embodiment) iscoupled between the input resistor and the output of the secondamplifier. The second amplifier 248 receives the error reference signalVref and the difference voltage Vd as described, and generates theskipping mode reference signal Vskip_mode as a function of thedifference between the difference voltage and the error referencesignal. Thus, the second amplifier 248 acts as a subtractor andsubtracts the error reference signal Vref from the different voltage Vd.The operation of the subtractor can be mathematically described as:

Vd−Vref=K1*√{square root over (Vout−Vin)}

The skipping more reference signal Vskip_mode can thus be mathematicallydescribed as:

Vskip_mode=K1*√{square root over (Vout−Vin)}

The circuits disclosed herein can help finely control the switchoverfrom PWM mode to PSM mode, and thus help reduce power consumption, asexplained above. Those of skill in the art will appreciate that thisdisclosure contemplates and covers related methods of circuit operation.

While the disclosure has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be envisionedthat do not depart from the scope of the disclosure as disclosed herein.Accordingly, the scope of the disclosure shall be limited only by theattached claims.

1. A circuit, comprising: a switching converter circuit configured tooperate in a pulse skipping mode to generate an output voltage from aninput voltage; an error amplifier configured to generate an error signalin response to a difference between a feedback voltage derived from theoutput voltage and a reference voltage; a first comparator configured togenerate a pulse skip mode control signal in response to a comparison ofthe error signal to a skip mode reference signal.
 2. The circuit ofclaim 1, wherein the switching converter circuit is further configuredto operate in a pulse width modulation mode and further comprising asecond comparator configured to generate a pulse width modulation modecontrol signal in response to a comparison of the error signal to apulse width modulation voltage signal.
 3. The circuit of claim 2,wherein the pulse width modulation voltage signal is a ramp signal. 4.The circuit of claim 1, further comprising a skip mode referencegenerator circuit configured to generate the skip mode reference signal.5. The circuit of claim 4, wherein the skip mode reference generatorcircuit comprises: a converter circuit configured to generate aconversion voltage as a function of a difference between the outputvoltage and the input voltage; and a differencing circuit configured togenerate a difference voltage as a function of a difference between theconversion voltage and the reference voltage, wherein the skip modereference signal is derived from the difference voltage.
 6. The circuitof claim 5, wherein the function of the difference between the outputvoltage and the input voltage is a square root function.
 7. The circuitof claim 5, wherein the skip mode reference generator circuit furthercomprises a subtraction circuit configured to generate the skip modereference signal by subtracting a fraction of the reference voltage fromthe difference voltage.
 8. The circuit of claim 7, further comprising aresistive divider circuit having an input configured to receive thereference voltage and an output configured to generate a voltage that issaid fraction of the reference voltage.
 9. The circuit of claim 5,wherein the converter circuit comprises: a first current generatorconfigured to generate a first current having a magnitude proportionalto the input voltage; a second current generator configured to generatea second current having a magnitude proportional to the output voltage;and a current summation circuit configured to generate a third currentas a function of a difference between the first and second currents. 10.The circuit of claim 9, wherein the converter circuit further comprisesa square root circuit configured to generate the conversion voltage. 11.The circuit of claim 11, wherein the square root circuit comprises: afirst transistor having a source-drain path; a second transistor havinga source drain path connected in series with the source-drain path ofthe first transistor at an output node; wherein the third current isapplied to the series connected source-drain paths and to controlterminals of the first and second transistors and the conversion voltageis generated at the output node.
 12. A method, comprising: operating aswitching converter circuit in a pulse skipping mode to generate anoutput voltage from an input voltage; determining a difference between afeedback voltage derived from the output voltage and a reference voltageto generate an error signal; and comparing the error signal to a skipmode reference signal to generate a pulse skip mode control signal forcontrolling operation of the switching converter circuit in the pulseskipping mode.
 13. The method of claim 12, further comprising operatingthe switching converter circuit in a pulse width modulation mode andwherein the pulse skip mode control signal control change of operationof the switching converter circuit between pulse width modulation modeand pulse skipping mode.
 14. The method of claim 12, further comprisinggenerating the skip mode reference signal from the input voltage andoutput voltage.
 15. The method of claim 14, wherein generating the skipmode reference signal comprises: generating a conversion voltage as afunction of a difference between the output voltage and the inputvoltage; and generating a difference voltage as a function of adifference between the conversion voltage and the reference voltage,wherein the skip mode reference signal is derived from the differencevoltage.
 16. The method of claim 15, wherein the function of thedifference between the output voltage and the input voltage is a squareroot function.
 17. The method of claim 15, further comprisingsubtracting a fraction of the reference voltage from the differencevoltage to generate the skip mode reference signal.
 18. The method ofclaim 15, wherein generating the conversion voltage comprises:generating a first current having a magnitude proportional to the inputvoltage; generating a second current having a magnitude proportional tothe output voltage; and generating a third current as a function of adifference between the first and second currents.
 19. The method ofclaim 18, further comprising determining the conversion voltage based ona square root of a signal generated in response to the third current.